CSRF in Jupyter Jupyterhub
CVE-2026-40864
JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately treated requests with Sec-Fetch-Mode: no-cors as same-origin requests, bypassing XSRF checks. The JSON API is not affected, only HTTP form endpoints, such as /hub/spawn and /hub/accept-share, meaning attackers could trigger server spawn (but not access the server) and if the attacker is a JupyterHub user permitted to share access to their server, cause a user to accept a share and have access to the attacker's server. This issue has been fixed in version 5.4.5. If developers are unable to immediately upgrade, they can temporarily mitigate this issue by dropping requests to JupyterHub with Sec-Fetch-Mode: no-cors if they are using a reverse proxy.
Vulnerability class: CSRF (Cross-Site Request Forgery)
EPSS: 0.002 (5.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L.
Affected products
- Jupyter Jupyterhub
- Jupyterhub — versions >= 4.1.0, < 5.4.5
Weakness classification (CWE)
Public proof-of-concept exploits
References
- security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-40864?
- CVE-2026-40864 is a medium-severity vulnerability in Jupyter Jupyterhub, classified under Cross-Site Request Forgery (CSRF). CVSS score: 5.4/10. Published 2026-05-22.
- How severe is CVE-2026-40864?
- Medium severity. CVSS v3 base score is 5.4 out of 10.
- Is CVE-2026-40864 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.